1. Field of the Invention
The present invention relates to a surface emitting laser which can emit laser beams in a direction perpendicular to a substrate, and more particularly, to a multi-wavelength surface emitting laser in which different types of surface emitting lasers emitting laser beams of different wavelengths are configured on the same substrate, and a method for manufacturing the same.
The present invention is based upon Korean Patent Application No. 00-41737, filed Jul. 20, 2000, which is incorporated herein by reference.
2. Description of the Related Art
In general, a surface emitting laser emits a laser beam in a direction normal to the surfaces of deposited semiconductor material layers, which is different from an edge emitting laser. Also, since the surface emitting laser emits a circular beam, unlike the edge emitting laser, an optical system is not needed to correct the cross-sectional shape of an emitted beam. Also, the surface emitting laser can be manufactured in a compact size, and a plurality of surface emitting lasers can be integrated on a single semiconductor substrate, thus enabling a two-dimensional arrangement. As a result, the surface emitting laser has a wide range of optical application fields such as electronic calculators, audio-visual apparatuses, laser printers, laser scanners, medical equipment, and communications apparatuses.
Referring to FIG. 1, a conventional surface emitting laser includes a substrate 10, a lower reflector 12, an active layer 14 and an upper reflector 16, which are deposited in order on the substrate 10.
The substrate 10 is formed of a semiconductor material such as gallium arsenide (GaAs) or indium phosphorous (InP) including a predetermined impurity, for example, an n-type impurity. The lower and upper reflectors 12 and 16 are distributed Bragg reflectors (DBRs) formed by alternately depositing pairs of semiconductor layers having different refractive indices. That is, the lower reflector 12 is formed on the substrate 10 and is formed of the same type of impurity as that of the substrate 10, for example, n-type AlxGa1-xAs and AlAs are alternately deposited. The upper reflector 16 is formed of the same semiconductor material as that of the lower reflector 12 and includes a semiconductor material with the opposite type of charge carriers to that of the lower reflector 12. For example, p-type AlxGa1-xAs and AlAs are alternately deposited. The active layer 14 has a single or multi-quantum well structure or a super lattice structure as an area for generating a light beam when energy transition is generated due to recombination of electrons and holes. An upper electrode 23 having a window 23a is provided on the upper surface of the upper reflector 16 and a lower electrode 21 is provided on the bottom surface of the substrate 10.
Also, to improve the output of light L emitted through the window 23a, a high resistance portion 18 is formed by injecting protons into the upper reflector 16 except for a zone under the window 23a. Accordingly, the high resistance portion 18 limits the flow of holes so that laser oscillation is generated only in the zone under the window 23a. 
In the surface emitting laser having the above structure, the wavelength of a laser beam is determined by the materials of the upper and lower reflectors 16 and 12, the structure of deposition, and the structure of the active layer 14. Thus, when the surface emitting laser is manufactured in a single process with a single substrate, it is difficult to produce the surface emitting laser in an array form so as to emit laser beams of different wavelengths.
Also, in application fields of a semiconductor laser capable of emitting laser beams having different wavelengths, such as compatible optical pickups for DVD players which can also read CDs, and communications equipment in which the wavelengths for transmitting and receiving are different, a structure in which surface emitting lasers, which are manufactured to correspond to desired wavelengths, and are attached to an additional substrate, has been suggested. However, the above structure has a problem in that it generates a large optical alignment error due to an error in the combination of the respective surface emitting lasers.